The Super Saiyan transformation comes in response to a need, not a desire. In all known cases, the form has been initially triggered by either desperation or indignation. Any other conditions are unknown, and motivation tends to differ; for example, Goku achieves the form out of anger over the murder of his best-friend Krillin and Bardock achieves the form out of anger after Chilled attacked a Plant child called Berry, while Vegeta achieves the form through sheer frustration at his original inability to achieve it, especially over Goku. While training in the Hyperbolic Time Chamber, Goku tells Gohan that becoming a Super Saiyan is powered by rage and told him to imagine Cell and then Frieza when Gohan said he had never seen Cell, killing all his friends to transform into a Super Saiyan.